AU694023B2 - Tin can with a foil closure membrane, and a process, device and foil for manufacturing the can - Google Patents

Abstract

The tin can is closed by a paper, plastic or metal-foil membrane (2) on at least one end face in such a way that the outer side of the foil edge region (5) raised in the direction of the can's axis (A) is joined to the essentially cylindrical inner surface of the wall of the can (1) to form a seal, without covering the wall edge of the can. The membrane foil (2) with the raised foil edge region (5) is introduced into the can and forced against the inner wall of the can (1) by a die (8) with an expandable periphery (17). Heat is then applied to create a sealing join between the raised foil edge region (5) and the inner wall of the can (1) without any external pressure-absorbing device.

Description

Can having a Foil Closure Membrane, and Process, Apparatus and Foil for the Production of the Can Background of the Invention Metal cans have to date been closed essentially either by flanging together the cut can edge with. a sheet metal lid (for example according to WO 83/02577 or US-A- 3,952,677) or by providing with a sheet metal ring provided with a foil (according to AT-A-368.919), or the inner surface of the can wall had to be conically shaped (for example according to DE-U-94 14 440), at least in the region of the raised foil edge which required more complicated can production and high tolerances to enable the same position of the diaphragm disc relative to the can edge always to be achieved on introduction of the punch.

On the other hand, discs with a raised edge which do not overlap the cut edge of the can have been disclosed for plastic cans (for example, DE-A1-33 05 144 or CH-A- 629 984), but these were always relatively stable lid parts for the bottom of cans capable of bearing a pressure load or those having a relatively soft wall (for example according to US-A-4,599,123), which required an external pressure absorption apparatus for the sealing, process.

In an inconvenient procedure employed to date, it was necessary to exert pressure externally against a fixed, stable punch applied in the interior of the (relatively I: 20 soft) cardboard can by bringing together annular segments or bringing together two conical surfaces.

A broad collar parallel to the diaphragm disc, as described, for example, in US- A-4,599,123, has proved to be extremely disadvantageous since, on introduction into the can without overlapping the cut edge of the can it must result in the formation of 25 creases, which make it more difficult, or even impossible, to achieve a tight connection between the foil and the inner surface of the can.

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2 Summary of the Invention It is the object of the present invention to overcome or substantially ameliorate the above disadvantages.

There is disclosed herein a method of producing a can, said method including 5 the steps of: a) providing a can wall section having an end section, an opposite end section and an irnner surface; b) providing a diaphragm closure having a periphery with a flange; c) introducing said closure into said can end section with said flange 1o extending away from said opposite end section; d) pressing said flange towards said inner surface by means of a punch operatively associated with an expandable periphery assembly to attach said flange to said inner surface, said attachment being effected without being opposed by a force from an external pressure absorption apparatus.

Preferably, said can wall section is made of sheet metal.

Preferably, said closure is made of paper.

More preferably, said closure is made of plastic film.

Even more preferably, said closure is made of metal foil.

Preferably, said can is cylindrical.

20 Preferably, said attachment of said flange to said inner surface is by means of adhesive bonding.

More preferably, said flange has a heat-seal coat and said flange is attached to said inner surface by means of heat-sealing.

Preferably, said flange extends approximately perpendicularly from said 25 diaphragm closure.

Preferably, said flange further includes a collar projecting radially outwardly therefrom.

Preferably, the closure is embossed or grained.

Preferably, said expandable periphery assembly includes at least one element adapted to translate an axial movement of said punch towards said can wall into an outwardly radial movement, so as to press said flange to said inner surface.

More preferably, said expandable periphery assembly includes a pneumatically operated rubber bellows attached to said punch.

There is further disclosed herein an apparatus for carrying out the method as described above, said apparatus having: a centering means for introducing the closure diaphragm to the can wall; a displaceably mounted punch axially aligned with respect to the centering I means; i iN:\LIBLO1608:PVH p 3 an expandable periphery assembly operatively associated with said punch; and a heating means for heating the expandable periphery assembly_ or an edge of said can wall adjacent said flange.

Preferably, said expandable periphery assembly includes at leE one element adapted to translate an axial movement of said punch towards said can into an outwardly radial movement so as to press said flange to said inner surface.

Preferably, said at least one element includes a plurality of wedges and piston rings or spring rings, said wedges being arranged radially inside of said rings, and wherein when said punch moves axially towards said can wall, said punch engages said wedges which in turn engages said rings, said rings pressing said flange to said inner surface.

More preferably, the expandable periphery assembly consists of rubber bellows arranged along the punch periphery and operated by a fluidic or pneumatic unit.

Preferably, said punch is situated radially inside of the centering means. ;j The diaphragm foil is preferably not more than 0.2 mm, more preferably not more than 0.1 mm, thick, consists, for example, of a 50 itm aluminium foil with prefer'ably a 20 mrn heat-seal coating on the inner surface and a 10-20 [uim antifriction coating on the outer surface and is therefore suitable for the closure of the subsequent 20 withdrawal opening. Depending on the contents or on a lid used, however, the can bottom, too, may be formed according to the invention, if required. Also preferred is the use of embossed foils because they can be more easily fitted closely to cans with changing tolerance and also give better stability.

In general, it is preferable if the diaphragm foil at least in the region intended 25 for connection to the inner surface of the can is coated with a heat-seal coating. In principle, however, the inner surface of the can may also be provided with a primer or a heat-sealable coat in the region mentioned as in the case of the inner surface of combination cans (for example, laminated with aluminium foil); otherwise, tight connection frequently requires the use of special in particular multicomponent 30 adhesives or heat-seal coatings. In any case, bright or coated cans can thus also be a. o closed with a tight seal.

Brief Description of the Drawings A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 shows the sequence of the method according to the invention, of which IN:\LIBLL101608:PVH 4 Figures 2 to 3 shows enlarged details II and III from Figure la and ib, respectively, while Figure 4 shows a section through the apparatus according to the invention.

3 Figures 5a and 5b show a horizontal section through the apparatus according to the invention, in two different operating positions.

Detailed Description of the Preferred Embodiment According to diagram a) in Figure 1, a can 1 of sheet metal is to be closed with a diaphragm foil 2. The foil 2 may be connected to a pull tab 3 in any desired manner, for example by adhesive bonding. In contrast to conventional pull tabs, the tab 3 can be used for pulling off the entire diaphragm foil 2 introduced into the can I and I connected to it at the edge. This is more advantageous because, in the conventional embodiment, it was necessary to provide either a predetermined breaking point, for example by punching, or a parting of the diaphragm foil edge overlapping the cut edge Sof the can from the diaphragm foil disc stretched over the can opening. In the case t rn i:: .o *d 'CP~ cc which, after thermoforming, is heat-sealed to the can inner wall in a broad gap between punch and can inner wall by expansion of the punch circumference.

A IDoad collar parallel to the diaphragm disc, as described, for example, in US-A-4,599,123, has proved to be extremely disadvantageous since, on introduction into the can without overlapping the cut edge of the can it must result in the formation of creases, which make it more difficult, or even impossible, to achieve a tight connection between the foil and the inner surface of the can.

There are of course a large number of possibilities according to the prior art for final mounting. However, since the foil used according to the invention is relatively thin and is preferably a foil having good thermal conductivity, use is made of a high-temperature joining process, for example the application of a heat-seal coating on the outer surface.

Further details of the invention are evident from the following description of embodiments illustrated in the drawing.

Fig. 1 shows the sequence of the process according to the invention, of which Fig. 2-3 show enlarged details II and III from Fig. la and Ib, respectively, while Fig. 4 shows a section through the apparatus according to the invention.

Fig. 5a and b show a horizontal section through the apparatus according to the invention, in two different operating positions.

According to diaphragm a) in Fig. I, a can 1 of sheet metal is to be closed with a diaphragm foil 2.

The diaphragm foil 2 may be connected to a pull tab 3 in any desired manner, for example by adhesive bonding.

In contrast to conventional pull tabs, the tab 3 can be used for pulling off the entire diaphragm foil 2 6 introduced into the can 1 and connected to it at the edge. This is more advantageous because, in the conventional embodiment, it was necessary to provide either a predetermined breaking point, for example by punching, or a parting of the diaphragm foil edge overlapping the cut edge of the can from the diaphragm foil disc stretched over the can opening. In the case of a thin foil of preferably not more than 0.2 mm, in general even not more than 0.1 mm, this always gave rise to difficulties.

Of course, such a thin foil which serves merely for maintaining freshness or preserving aroma or for preventing contamination is relatively difficult to handle. According to the invention, it now has, along the circumference of a cover region 4, a foil edge region 5 which is raised all around and imparts a certain rigidity to the diaphragm disc part stretched over the can opening. For imparting rigidity (and also for achieving a slight, radial elasticity during deep drawing and/or sealing), the diaphragm foil 2 closing the bottom of the can preferably has at least one annular bead. The diaphragm foil 2 reinforced in this manner can now be picked up in an interlocking manner (so that the foil shape is not changed on insertion into the can opening), for example by means of a suction gripper known per se, and can be mounted on the top of the can 1 in a first step. Here, a further Sdifficulty associated with a thin foil is encountered: it is in fact necessary to ensure that the foil remains on the top of the can 1 so that it can be tightly connected to the inner surface of the can in the next step. It would be possible in principle to provide the upper edge of the can 1 with an adhesive so that the film remains attached thereto in the desired position.

However, this is advantageously effected according to the invention in a manner more readily evident from Fig. 2.

7 In said figure, the raised edge is at least slightly conically divergent, i.e. there is an angle B with the vertical V, which angle, although only very small is still measurable and has a magnitude of less than 50, in particular less than 20. In a practical embodiment, the diameter of the lower surface of the diaphragm disc, i.e. in the region of the cover surface 4, is only a few tenths of a millimetre smaller than the opening diameter of the diaphragm disc, it being necessary for the height measured along the vertical V to be only about 5 mm.

The upper, larger diameter of the diaphragm foil 2 is of course expediently chosen so that, when mounted, it is held on the top of the can 1 by the suction gripper by means of frictional force. A further measure for securing the diaphragm foil 2 on the top of the can 1 may consist in a collar 6 which has a hook-shaped cross-section and interacts with the upper edge of the can 1. The upper, generally sharp edge of the can 1 is furthermore preferably flanged towards the outside (7 in Fig. la, in order to prevent damage to the thin foil or injury to the user.

The diaphragm foil 2 thus fits with this collar 1 6 firmly on the edge of the can. However, this is only an intermediate step in the closing of the can 1 and should not hinder the subsequent steps. This includes the action of a punch 8 which is shown only 'schematically in Fig. lb and presses the diaphragm foil 2 into the position shown in Fig. lb. The collar 6 slides from the position indicated by a dash-dot line in Fig. 3, in which it was present before being pressed down by the punch 8, into the interior of the can and, owing to the ductility of the foil material (with simultaneous sufficient toughness), assumes the position, indicated in Fig. 3 by solid lines, at the inner circumference of the can 1. The conical shape of the film edge region 5 with the small angle B, which 8 shape is shown in Fig. 2, becomes a cylindrical shape, so that the film edge region 5 is in close contact with the can circumference. As a result of the slightly conical shape, the formation of creases and wrinkles -as mentioned expressly in US-A-4,599,123 is avoided.

As described below, the process according to the invention and the apparatus according to the invention a result in a tight connection between the diaphragm foil g 2 and the cylindrical region of the inner surface of the can immediately below the (preferably flanged) can edge: In a preferred embodiment, the punch 8 is formed according to the section shown in Fig. 4. It consists j of several parts, namely the actual punch surface 9, A which is connected to the lug 11 of a punch head 12 by means of upward-projecting pins 10 (only one is shown, but there are preferably three). A centring ring 13 is *placed around the punch surface 9 and can be moved Salong guide pins 14 and against the action of at least one pressure spring 15. Usually, the ring 13 assumes the lowered position on the left in Fig. 4, in which, for example, it is supported on the upper side of the punch surface 9 in a manner not shown, but optionally is also held by other means.

In this position, the centring ring 13 holds the can edge, and has a recess 13' for this purpose. The process can now take place in such a way that the can 1 V stands on a lifting table and is raised, with the result that the centring ring 13 is displaced against the action of the spring 15 to the upper position shown on the right. At the same time, the punch surface 9 emerges from the interior of the ring 13 and thus presses the diaphragm foil 2 into the position shown in Fig. lb and 3.

Alternatively the ring 13 could also be stationary and the can held in a centred position while the punch surface 9 is moved downwards. In this case, c j 9 it would be necessary, for example, for the lug 11 to be in the form of a piston rod of a fluidic aggregate, preferably of a pneumatic piston/cylinder aggregate.

However, it is clear that in this case further latitude is allowed as a result of design considerations, since in fact only the relative movement of the parts shown and the can is important. Furthermore, the centring of the can, or of the diaphragm foil 2 relative to it, could be carried out in various ways.

From the above explanations, it is clear that it I is important to position the raised foil edge region of the diaphragm foil 2 as close as possible to the inner circumference of the can (as shown in Fig. 3) in i, order to connect said edge region firmly to said inner circumference. For this purpose, the punch 8 has a spreading device, which is formed by a wedge arrangement in the embodiment according to Fig. 4. A Srow of wedge segments 16 is guided along the upper side f of the punch surface 9 in such a way that they can be Sdisplaced radially outwards with respect to the central j axis A of the punch 8. For guidance, the back of the i punch surface 9 could have, for example, grooves or slots (not shown). However, the flat back of the punch Ssurface may also be sufficient for guidance.

Although the wedge segments 16 as such could themselves be used for pressing the raised foil edge region 5 of the diaphragm foil 2 against the inner circumference of the can 1, it is advantageous if elastic piston rings 17 or Seeger circlip rings are stretched around them. This provides a more uniform circumferential area when these rings 17 are pressed against the foil edge region 5 of the diaphragm foil 2 and moreover perfoims a dual function by also generating a restoring force which acts on the segments 16.

A conical wedge 18 is provided for pressing wedge segments 16 radially outwards, which wedge can be moved downwards and between the wedge segments with their wedge surfaces 20, by means of an actuating rod 19 of a drive, preferably of pneumatic type. The reason for preferring a pneumatic drive is that there is scarcely any danger of soiling by oil or leaked liquid and it is particularly easy to set a maximum pressure which does not extend the can. When the conical wedge 18 is moved downwards against the punch surface 9, it spreads apart the wedge segments 16 and thus presses the elastic rings 17 against the foil edge region 5 (which is partially indicated in the bottom right of Fig. 4) in an outward direction, where the can edge fits firmly in the recess 16". The position of the diaphragm foil 2 according to Fig. Ib is reached in this way.

In this position, however, the diaphragm foil 2 must also be secured and in general also sealed. This can be effected in a conventional manner by means of adhesive bonding, preferably by means of heat-sealing, because the thin diaphragm foil 2 does in fact transmit the heat relatively readily. For this purpose, the outside of the film edge can be provided with a heatseal coat 21 (Fig. A heating means is then coordinated with the spreading apparatus 16-18. Said heating means could be formed per se by heating coils 3 housed in the wedge segments 16, but space is very limited there, and it is also necessary to provide movable connections. Although this possibility should therefore not be ruled out, it is possible to provide a radiant heat source 22 (for example, an annular one), for example above the wedge segments 16 and the ring 17, which heat source heats these parts in order to warm up the heat-seal coat 21 (Fig. 2) and to fuse it with the inner surface of the can 1. The wedge segments 16 may be formed, for example, from a ceramic material having good--_heat -storage properties, which also improves the wear properties.

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.1 11 Fig. 5a shows the wedge segments 16 and a spring ring 17 in the closed position and Fig. 5b shows them in the position in which they are spread (by the wedge pieces 18 of the punch 8 which is not shown here and is moved at right angles to the plane of the drawing) for the purpose of heat-sealing the diaphragm foil 2 to the inner surface of the can.

It is clear that the wedge arrangement shown is only one possible embodiment which may be preferred with regard to the life of the apparatus, and that many modifications are possible within the scope of the invention. For example, the conical wedge 18 could simply be formed by a pressure plate which is movable relative to the punch surface 9, it being possible to provide a rubber bellows between the upper side of the punch surface 9 and the pressure plate. Said bellows expands laterally from the top on being supplied with a pressure medium through the pressure plate which is used instead of the part 18 and which then would also be connected to the rod 19 for actuating the latter, and thus presses on the displaceable parts 16 or directly on the ring 17. A horizontal drive extending radially outwards would also be possible for the individual segments 16, but would be of complicated design. Particularly in this case, but also in other cases, heating of the upper can edge from the outside for heat sealing may be the simpler solution.

As soon as the can 1 is closed in the position 4A according to Fig. Ib, further, additional measures may 14 be advantageous. For example, in order to protect the vulnerable diaphragm foil 2, a lid 2, or 24 (Fig. Ic) can also be mounted.

Another particular advantage of the present invention is that the foils can be separately produced and, if necessary, kept in stock, and where the cans 1 are of identical diameter cans having different volumes can be equipped with the foils 2 which are 1/ Sr LJ) 12 produced beforehand and, owing to their design with the foil edge region 5, are in fact sufficiently stable.

This foil edge region 5 can also be readily coated with the adhesive 21, which would be difficult to apply to the inner circumference of the can, owing to the danger of soiling. On the other hand, the invention is of course not limited to the use of an adhesive, as already explained.

The invention is not limited to the embodiments described. Thus, the output of the apparatus according to the invention with multiple tools for example, arranged on a turntable can be increased in a manner known per se.

Claims (20)

1. A method of producing a can, said method including the steps of: a) providing a can wall section having an end section, an opposite end section and an inner surface; b) providing a diaphragm closure having a periphery with a flange; c) introducing said closure into said can end section with said flange extending away from said opposite end section; d) pressing said flange towards said inner surface by means of a punch operatively associated with an expandable periphery assembly to attach said flange to 1 o said inner surface, said attachment being effected without being opposed by a force from an external pressure absorption apparatus.

2. The method of claim 1 wherein said can wall section is made of sheet metal.

3. The method of claim 1 or 2 wherein said closure is made of paper.

4. The method of claim 1 or 2 wherein said closure is made of plastic ~film.

The method of claim 1 or 2 wherein said closure is made of metal foil.

6. The method of any preceding claim wherein said can is cylindrical.

7. The method of any preceding claim wherein said aatachment of said flange to said inner surface is by means of adhesive bonding.

8. The method of any one of claims 1 to 6 wherein said flange has a t heat-seal coat and said flange is attached to said inner surface by means of heat-sealing.

9. The method of any preceding claim wherein said flange extends approximately perpendicularly from said diaphragm closure.

10. The method of any preceding claim further including a collar projecting radially outwardly from the flange. i'

11. The method of any preceding claim wherein the closure is embossed t or grained.

12. The method of any preceding claim wherein said expandable periphery 30 assembly includes at least one element adapted to translate an axial movement of said punch towards said can wall into an outwardly radial movement, so as to press said flange to said inner surface.

13. The method of any one of claims i to 11 wherein said expandable periphery assembly includes pneumatically operated rubber bellows attached to said punch.

14. An apparatus for carrying out the method as described in any preceding claim, said apparatus having: "-77 Z_,a centering means for introducing the closure diaphragm to the can wall; [N:\LIBLL]01608:PVH \U- a displaceably mounted punch axially aligned with respect to the centering means; an expandable periphery assembly operatively associated with said punch; and a heating means for heating the expandable periphery assembly or an edge of said can wall adjacent said flange.

The apparatus of claim 14 wherein said expandable periphery assembly includes at least one element adapted to translate an axial movement of said punch towards said can wall into an outwardly radial movement so as to press said flange to said inner surface. 1o

16. The apparatus of claim 15 wherein said at least one element includes a plurality of wedges and piston rings or spring rings, said wedges being arranged radially inside of said rings, and wherein when said punch moves axially towards said can wall, said punch engages said wedges which in turn engages said rings, said rings pressing said flange to said inner surface.

17. The apparatus of claim 14 wherein the expandable periphery assembly consists of rubber bellows arranged along the punch periphery and operated by a fluidic or pneumatic unit.

18. The apparatus of any one of claims 14 to 17 wherein said punch is 20 situated radially inside of the centering means.

19. A process substantially as hereinbefore described with reference to the 'accompanying drawings. o

20. Apparatus substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings. 25 Dated 27 May, 1998 SiWerner Grabher S Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON IN;\LIBLLI01608:PVH